Why do car seatbelts have one strap whereas airplane pilot seatbelts have two straps?
In: Engineering
It’s a cost/function formula.
Let’s start with planes: There are three types (oversimplifying) of seat belts. Planes don’t crash very often, so the seat belts aren’t about saving your life in the event of a crash. They do, however, experience turbulence, shaking the plane pretty badly. If you look at a passenger seat, it’s just a single strap to keep you from flying out of your seat when the plane drops. It’s the cheapest option, but as effective as it needs to be. The stewardesses get two straps to hold the upright while rear facing. This lets them have a good idea of what is going on in the plane, even in an emergency. Then, move to the pilots, and they have a 5 point harness. As the plane drops or shakes, they need to be upright, in place and able to control the plane.
Now, as we move to a car, you’ll notice a two strap system in most passenger vehicles. Cars are more likely to crash than a plane, and passengers are more likely to survive. These three point systems hold you in place to prevent whiplash and other spine injuries. However, since most of the time you’re not in an accident, they are flexible enough to let you comfortably move around. In the case of a crash, the driver mostly needs to be able to hit the breaks and remain in their seat, so a 5 point harness is overkill. A simpler belt will be more likely to be used, and doesn’t loose much over a 5 point, plus is cheaper and fits more people.
We’ve actually seen a move from a single strap seatbelt for cars, to the two belt system in the front seat, to a two belt system in 2 of the three rear seats as well, to now almost all cars have a two belt system in all three seats. This is because cars are generally traveling faster, and are safer and are more expensive. You’re more likely to survive the impact, and it will have more force, so there is an added benefit to a more secure strap – with cars costing more, you’re less likely to notice the extra cost.
Further proof: race car drivers use the 5 point harness. They are going faster, subjected to stronger forces, and need to have control of their car in much more extreme scenarios. Plus, the cars are built for them, so the straps don’t need to be as easily adjustable. They aren’t reaching in the back for a soda, or adjusting the radio – so comfort isn’t as important.
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